1. Field of the Invention
The present invention relates to liquid injection nozzles, and more particularly, to pressure atomizing nozzles for injecting fuel for combustion.
2. Description of Related Art
A variety of devices are known for injecting and atomizing liquids. For example, pressure atomizing nozzles can be used to inject an atomized spray of fuel to be combusted in a furnace, gas turbine engine, or the like. The harsh environment of combusting fuel gives rise to difficulties associated with the breakdown of fuel at high temperatures. Hydrocarbon fuels tend to decompose when heated. At elevated temperatures below about 800° F., dissolved oxygen in the fuel forms coke deposits. At temperatures above about 800° F., pyrolysis occurs leading to carbon deposits. Coke deposits tend to form on internal nozzle surfaces, and carbon deposits tend to form on external nozzle surfaces. Coke and carbon deposits are each described in greater detail below. These problems give rise to a need to replace or clean nozzles operating in combustion environments which results in expense and/or downtime that could otherwise be avoided.
With respect to coke formation, intricate fuel passages of typical atomizing nozzles are susceptible to the formation of coke when heated to sufficient temperatures. This is particularly a problem when stagnant fuel in the fuel passages is heated, such as just after an engine is shut down, or when an engine is running with staged fuel injection so that some fuel passages are stagnant during operation. Coke deposits accumulate in nozzle tip openings and intricate fuel passages and if left unchecked can lead to inadequate flow and even complete blockage of flow.
With respect to carbon deposits, the deposition of carbon on exposed nozzle surfaces, e.g., soot deposits, can occur wherever relatively cool surfaces are exposed to combustion products. When fuel is running through a typical nozzle with combustion occurring just downstream of the nozzle, the nozzle is cooled by the fuel flowing therethrough. Carbon released from the fuel by pyrolysis, coming into contact with the relatively cool exposed surfaces of the nozzle, can condense and form a carbon deposit thereon. Similar to coke deposits, carbon deposits can alter nozzle geometry and therefore hinder proper functioning.
Some solutions to these problems have been practiced with some success. For example, one approach is to use a local thermal heater to systematically burn carbon and coke from the nozzle tip to keep the nozzle free of contamination. However, the heater approach is relatively expensive and introduces its own reliability issues.
Such conventional methods and systems have generally been considered satisfactory for their intended purposes. However, there is still a need in the art for nozzles that allow for improved reduction and/or prevention of carbon and coke deposition, including by passive means. There also remains a need in the art for such nozzles that are easy to make and use. The present invention provides a solution for these problems.